The invention is based on an oil separator for crankcase gases of an internal combustion engine, comprising a preliminary separator, a cyclone separator, a fine separator and, if necessary, a valve device that are provided in a cascade arrangement on a cylinder-head hood of the internal combustion engine.
When an internal combustion engine operates, streams of blowby gas are produced between pistons, piston rings, and cylinder walls and, if applicable, in the region of valve guides. This blowby gasxe2x80x94which enters the crankcase or a camshaft housing, or travels above the cylinder head or is guided therexe2x80x94contains fluid components, primarily fine oil droplets or motor oil components with a low boiling point. Larger oil droplets can also be contained in the crankcase gas or even in the camshaft housing gas that are produced by moving drivetrain parts, i.e., piston, connecting rod, crankshaft or camshaft. This is also referred to as xe2x80x9cswirl oilxe2x80x9d. In order to remove the blowby gases, a venting of the crankcasexe2x80x94which usually extends over the camshaft housingxe2x80x94is provided. These gas/fluid quantities referred to as crankcase gas and occurring intermittently are separated from the fluid components by means of an oil separator and then typically directed to the intake region of the internal combustion engine. By separating the oil, dirt is prevented from accumulating in the downstream regions, and the emission of hydrocarbons is not increased in an undesired fashion.
An oil separator for crankcase gases of the generic type is made known in DE 197 00 733 A1. This publication discloses and teaches that the components of the oil separator named initially are to be located in the cylinder-head hood of the internal combustion engine. The preliminary separator and the cyclone separator are located on the inside of the cylinder-head hood, i.e., on the side of the cylinder-head hood facing the crankcase and/or camshaft housing. The fine separator and the valve device are located between two housing cover halves of the cylinder-head hood and are located downstream from the cyclone separator in terms of flow. Moreover, with this known oil separator, an oil return opening to the camshaft housing is formed in the region below the fine separator insert of the fine separator. Fluid, particularly oil, that was separated out in the preliminary separator and in the cyclone separator travels through angular housing passages and reaches the housing region of the fine separator and, from there, is directed via the oil return opening mentioned hereinabove back into the camshaft housing. Separated fluid from three stages is therefore collected via the oil return opening in the third stage. The separated fluid can interfere with the flow inside the oil separator and, in fact, precisely when large quantities of fluid are separated. Moreover, the rapid flowxe2x80x94particularly with or at the end of the cyclone separatorxe2x80x94can interfere with the return of separated fluid.
Based on this, the object of the invention is to overcome this disadvantage.
This object is attained with a generic oil separator according to the invention by providing an oil drain opening upstream from the cyclone separator in the flow or cascade direction, through which oil separated in the preliminary separator can be returned.
It is therefore proposed that oil separated in the preliminary separator be returned directly to the engine compartment via a further return opening. This is easily possible, because a notable pressure differential does not yet exist in the region of the preliminary separator, and the quantity of fluid separated there can simply drip or run downward, and it is not carried with the flow into the preliminary separator. In this fashion, a large portion of the fluid contained in crankcase gas, i.e., larger oil droplets, are separated out in advance and returned directly to the engine compartment. The same opening in the cylinder-head hood is preferably used for the return, running-off or dripping of this quantity of fluid as well as directing the crankcase gas into the oil separator. This opening preferably has a large opening cross-section that can comprise, for example, a draining wallxe2x80x94that is domed, in particularxe2x80x94projecting into the camshaft housing space, which said draining wall is formed by the cylinder-head hood.
In a further development of the invention, the oil separator is designed so that the preliminary separator, the cyclone separator, the fine separator and the valve device that is provided if necessary are located on the outside of the cylinder-head hood and are covered by a housing half-shell which, together with the outside of the cylinder-head hood, forms a housing for the separator and can be installed on the outside of the cylinder-head hood in sealing fashion.
The arrangement of the components of the oil separator outside of the actual cylinder-head housing opens up the possibility of producing all components in one housing, i.e., a housing half-shell of the oil separator, as a subassembly that can be pre-assembled, and then adjoining this subassembly in entirety, in modular fashion, with or without an additional bottom part, to the outside of the cylinder-head hood. In particular, the cylinder-head hoodxe2x80x94detached from components of the oil separatorxe2x80x94can be installed on the cylinder head in order to seal off the top of the camshaft housing. The preassembled subassembly of the oil separator can then be installed at this time or a later time.
It is found to be particularly advantageous when the housing half-shellxe2x80x94which forms a housing for the oil separatorxe2x80x94is a plastic part produced as a single component, in particular an injection-molded part.
With regard for the ability of the oil separator to be preassembled in specific subassemblies, it is found to be particularly advantageous when flow guide walls of the preliminary separator, a helical insert for the cyclone separator, a separator insert for the fine separator, and preferably the valve device as well, can be placed in the housing half-shell for preassembly. All components with regard for the housing half-shell can then be preassembled, stockpiled as ready-to-install subassemblies, and then delivered to the cylinder-head hood at the desired point in time for final assembly.
The housing half-shell should be advantageously designed rather flat and elongated in shape. To handle crankcase gases of up to 150 l/min, a diameter of only approximately 295xc3x9760xc3x9770 mm (lengthxc3x97widthxc3x97height) has been found to be sufficient; with this, it was possible to separate oil quantities of 100 to 200 g/h. In order to obtain these quantities using non-generic, modular designs of externally adjoined cyclone separators, a much greater overall height of 175 mm and a length and width of 105xc3x9790 mm was required until now. The design according to the invention makes it possible to realize pancake-designed, elongated dimensions when configuring the oil separator in the range described hereinabove, which said dimensions are sufficient in terms of their efficacy, throughput rate, and separation capacity.
It is found to be advantageous when the housing half-shell comprises circumferential side walls extending in the direction toward the cylinder-head hood that transition into a full-perimeter, front edge facing the cylinder-head hood, with which the housing half-shell can be placed against the outside of the cylinder-head hood in sealing fashion.
This full-perimeter, front edge can advantageously define a seating plane, which then makes it necessary to design the outside of the cylinder-head hood correspondingly flat in the region where the oil separator is installed. A design of the housing half-shell of the oil separator having circumferential side walls extending in the direction toward the cylinder-head hood, i.e., having a substantially pot-shaped geometry, makes it possible in particularly advantageous fashion to preassemble all components in the protected and prefabricated housing, which then only need be joined with the outside of the cylinder-head hood via its full-perimeter edge. As an alternative or in addition, a bottom part could close the housing half-shell of the subassembly, in particular except for afflux and return openings.